Foam with filling

ABSTRACT

The present invention relates to open-cell foams filled with polyamide and also to a production process therefor.

The present invention relates to open-cell foams filled with polyamideand also to a production process therefor.

There are various known prior art processes composed of polymericmaterials for example. An overview of various types of foams is, forexample, “Polymeric Foams and Foam Technology”, edited by D. Klempnerand V. Sendijarevic, Carl Hanser Verlag, Munich, 2nd edition, 2004. Here“foam” can be defined as a material produced by incorporation of gasbubbles into a liquid or solid.

Open-cell foams are also known in principle. The term “open-cell”defines a foam structure wherein every cell includes at least two poresor destroyed faces. In addition, a majority of cell ribs have to formpart of three cells at least. In closed-cell foams, by contrast, thecells do not have any pores or destroyed faces. Open-cell plastics foamsare usually produced on the basis of polyethylene (PE), polyurethane(PU) and polyvinyl chloride (PVC), see Arnim Kraatz's thesis, 2007,Halle University). Typically, an open-cell foam tends to be soft.

Open-cell foams can consist of metals or of plastics materials forexample.

Processes are described in the prior art for modifying the properties ofa thermoplastic or of a thermoset via inclusion of other substances.Examples of processes of this type are mixing with another polymer toform a homogeneous system (e.g., PMMA and PSAN, or PPO andpolystyrene—see Modern Styrenic Polymers, John Wiley and Sons, Ltd,2003, page 699, part 6, Styrenic Blends), adding lubricants to enhanceflowability (Plastics Additives Handbook, 5th Edition, HanserPublishers, Chapter 5, Lubricants), adding glass fibers to enhancestiffness (Handbuch der Technischen Polymerchemie, VCH Verlag, 1993,page 651, part 12.4.5.1, reinforced plastics), and incorporating rubberinto a rigid thermoplastic to modify compressive strength and toughness(Mechanical Properties of Polymers Based on Nanostructure andMorphology, Taylor and Francis Publishers, 2005, Chapter 11,Structure-Property Relationships in Rubber Modified AmorphousThermoplastic Polymers.

Inclusion of other substances, for example polymers, in a polymeric foamcan often provide a mutual improvement in the mechanical properties ofthe various components, i.e., the foam and the polymeric substanceincluded in the foam (reinforcing effect). In some cases, for example,melting of the foam at low temperatures is prevented or flame resistanceis improved.

Existing processes, which are mostly injection-molding processes, areincapable of providing an interpenetrating network of a foam withpolymers, since the viscosity of polymers is generally too high. Thepores of a foam can only be filled incompletely with a polymer, if atall, using existing processes. Moreover, attempts to fill the pores of afoam will often damage or destroy the foam.

It is an object of the present invention to provide a process forfilling the pores of an open-cell foam with a polymer as completely aspossible without damaging the foam in the attempt. This should provide acomposite material having improved properties, for example improvedmechanical properties, such as toughness, extensibility and recoveryafter compression.

We have found that this object is achieved, surprisingly, by thecatalyzed anionic polymerization of lactam monomers in the presence ofopen-cell foams.

The present invention accordingly provides a process for producing acomposite material comprising drenching an open-cell foam (S) at leastin part with at least one monomer (M) from the group of lactams and thenpolymerizing the monomer (M) at least partially anionically using acatalyst.

Further subjects of the present application are a composite materialobtainable by the process of the present invention and also the use of acomposite material obtainable by the process of the present invention insports equipment, as a flameproofing element or as a reinforcingelement.

In preferred embodiments of the present invention, one of the phaseseffectuates a positive modification of the other (mutual reinforcingeffect). This effect can be exploited, for example for reinforcement,impact modification or improving the breaking extension of a compositematerial. A further advantage is the reduced water imbibition of thecomposite material of the present invention compared with conventionallyproduced composite materials.

The term “composite material” herein refers to an engineering materialcombining two or more dissimilar constituent materials.

The term “melamine-formaldehyde foam” comprises melamine-formaldehydecondensates which, in addition to melamine, may comprise up to 50% byweight and preferably up to 20% by weight of other compounds, capable offorming heat-curable resins, and which, in addition to formaldehyde, maycomprise up to 50% by weight and preferably up to 20% by weight of otheraldehydes as co-condensed units.

However, the use of an unmodified melamine-formaldehyde condensate ispreferred according to the present invention.

Examples of other compounds capable of forming heat-curable resins aremelamine substituted by alkyl, urethanes, aliphatic amines, phenol andphenol derivatives. Examples of useful aldehydes are acetaldehyde,acrolein and benzaldehyde.

Further details concerning melamine-formaldehyde condensates arediscernible from Houben-Weyl, Methoden der organischen Chemie, volume14/2, 1963, page 319 to 402.

The molar ratio of compound capable of forming heat-curable resin toaldehyde can be varied within wide limits from 1:1.5 to 1:4.5; in thecase of melamine-formaldehyde condensates it is preferably in the rangefrom 1:2.5 to 1:3.5.

The melamine resins advantageously comprise co-condensed sulfite groups.Further details concerning melamine-formaldehyde condensates are alsodiscernible from U.S. Pat. No. 4,540,717.

After the process of the present invention, the foam and the polyamideeach form a continuous phase. Thus, at the end of the process, thesystem comprises at least two co-continuous phases, or at least two mainphases. It is believed that the morphology of the composite material ofthe present invention is mainly determined by the pore size.

Specifically, the process of the present invention is carried out asfollows. The foam therein is preferably dry.

The foam (S) is contacted with a mixture, for example a solutioncomprising monomer (M), catalyst and optionally activator. This can beaccomplished for example by dipping the foam into a solution of monomer(M), catalyst and optionally activator, or by spraying the foam (S) withthis solution, or by brushing the foam with the solution. This step ispreferably carried out under reduced pressure.

The temperature for the subsequent polymerization is generally in therange from 85° C. to 200° C., preferably in the range from 95° C. to180° C. and more preferably in the range from 105° C. to 160° C.

The monomer (M) may be situated exclusively in the pores of the foam(S). However, it can also be advantageous to have a thin polymeric filmon the surface of the foam (S) and hence of the composite (W).

The ratio of foam (S) to monomer (M) can be varied. The ratio isgenerally in the range from 90:10 to 10:90, preferably in the range from80:20 to 20 to 80 and more preferably in the range from 60:40 to 40:60.

According to the present invention, the foam may consist for example ofmetal, plastic or of a natural product such as wood (balsa wood forexample). The foam may also consist of mixtures of these materials.

In a preferred embodiment, the foam consists of metal or of mixtures ofplastic with metal. Metals from the group comprising aluminum andmagnesium are preferred.

In a further preferred embodiment, the foam consists of plastic.

Examples of plastics capable of forming suitable foams are PSU(polysulfone), PEI (polyetherimide), PI (polyimide), polyurethanes, PA(polyamide), PLA (polylactide), PPE/PS (polyphenyleneether/polystyrene), amsan (acrylonitrile/alpha-methylstyrene), PC(polycarbonate), polypropylene, melamine-formaldehyde.

Particular preference is given to melamine-formaldehyde foam, forexample Basotect® from BASF SE.

According to the present invention, the foam should be thermally stableup to 90° C., preferably up to 105° C. and more preferably up to 130° C.

The foam may have a regular or irregular pore structure. An example ofthe latter is a honeycomb structure that occurs in beehives for example.This structure usually possesses a hexagonal pore structure.

Monomer (M) is a compound from the group of lactams. Examples thereofare caprolactam, piperidone, pyrrolidone, laurolactam or mixturesthereof, preferably caprolactam, laurolactam or mixtures thereof andmore preferably caprolactam or laurolactam.

Useful catalysts include inter alia sodium caprolactamate, potassiumcaprolactamate, bromide magnesium caprolactamate, chloride magnesiumcaprolactamate, magnesium biscaprolactamate, sodium hydrides, sodiummetal, sodium hydroxide, sodium methoxide, sodium ethoxide, sodiumpropoxide, sodium butoxide, potassium hydride, potassium metal,potassium hydroxide, potassium methoxide, potassium ethoxide, potassiumpropoxide and potassium butoxide, preferably sodium hydrides, sodiummetal, sodium caprolactamate and more preferably sodium caprolactamate(e.g., Bruggolen® C 10, a solution of 18% by weight of sodiumcaprolactamate in caprolactam).

A preferred embodiment of the present invention utilizes at least oneactivator (also known as an initiator). However, it is not absolutelynecessary to use an activator.

Useful activators include inter alia aliphatic diisocyanates such asbutylene diisocyanate, hexamethylene diisocyanate, octamethylenediisocyanate, decamethylene diisocyanate, undodecamethylenediisocyanate, dodecamethylene diisocyanate, or else aromaticdiisocyanates such as toluyl diisocyanate, isophorone diisocyanate,4,4′-methylenebis(phenyl isocyanate), 4,4′-methylenebis(cyclohexylisocyanate) or polyisocyanates such as isocyanates of hexamethylenediisocyanate, Basonat® HI 100 from BASF SE, allophanates such as ethylallophanate or mixtures thereof, preferably hexamethylene diisocyanate,isophorone diisocyanate, and more preferably hexamethylene diisocyanate.Useful activators further include acyl halides or any reaction productsof acyl halides or isocyanates with lactams.

The molar ratio of lactam to catalyst can be varied within wide limits,and is generally in the range from 1:1 to 10 000:1, preferably in therange from 10:1 to 1000:1 and more preferably in the range from 50:1 to300:1. The molar ratio of activator to catalyst can be varied withinwide limits, and generally is in the range from 100:1 to 1:10 000,preferably in the range from 10:1 to 1:100 and more preferably in therange from 1:1 to 1:10.

On completion of the process according to the present invention, i.e.,after the polymerization of monomer (M) has ended, the compositematerial can be optionally also postformed, for example by heating andbending.

The composite material obtainable by the process of the presentinvention is very useful inter alia as a flameproofing element orreinforcing element, for example in automotive construction, or insports equipment.

EXAMPLES

The examples which follow serve to illustrate some aspects of thepresent invention. They should in no way be deemed to restrict the scopeof the invention. All components and apparatus items were dry.

Example 1

A foam composed of Basotect® (a flexible, open-cell foam of melamineresin) measuring 55×20×95 mm³ was laid into a dish formed from aluminumfoil and measuring 65×30×105 mm³. The dish was placed for several hoursinto a drying cabinet at 150° C. under nitrogen.

The following solutions were prepared separately in two glass flasksunder nitrogen:

1: 38.45 g of caprolactam+11.55 g of Bruggolen® C10 (a catalyst forpreparing polyamide from Brüggemann; 17% of sodium caprolactam incaprolactam)

2: 44.89 g of caprolactam+5.11 g of Bruggolen® C20 (an activator forpreparing polyamide from Brüggemann; 80% blocked diisocyanates incaprolactam),

and melted by means of a magnetic stirrer. At 110° C. solutions 1 and 2were mixed, commixed for 15 seconds and then added to the aluminum dishin the drying cabinet under N₂ until the dish was full. Excess liquidwas removed by briefly shaking. After 10 minutes the polymerization hadended. The aluminum dish was taken from the drying cabinet and cooled.The molded article was removed from the aluminum dish. It consisted ofan interpenetrated network of foam (Basotect® of BASF) filled withpolycaprolactam. VN (viscosity number)=180, residual caprolactam=1.9% byweightThe density of the molded article was 1.1 g/mL.

Example 2

An open-cell foam of polyamide (PA) measuring 55×20×95 mm³ was put intoa glass flask. The flask was evacuated for several hours at 150° C.

The following solutions were prepared separately in two glass flasksunder nitrogen:

1: 38.45 g of caprolactam+11.55 g of Bruggolen® C10

2: 44.89 g of caprolactam+5.11 g of Bruggolen® C20,

and melted by means of a magnetic stirrer. At 110° C. solutions 1 and 2were mixed, commixed for 15 seconds and then added to the PA foam via avalve. After 10 minutes the polymerization had ended.

A microscopic cross section through the foam showed that there was aninterpenetrating network.

Before and after the treatment with the caprolactam monomer, the foamwas immersed in water for 30 minutes in each case. It was found thatwater imbibition was distinctly higher before the treatment than after.

Similarly, the stiffness of the foam was distinctly higher after thecaprolactam polymerization than before.

1. A process for producing a composite material comprising drenching anopen-cell foam (S) at least in part with at least one monomer (M) fromthe group of lactams and then polymerizing the monomer (M) at leastpartially anionically using a catalyst.
 2. The process according toclaim 1 wherein the foam (S) consists of plastic and/or metal.
 3. Theprocess according to claim 1 or 2 wherein the foam (S) is amelamine-formaldehyde foam.
 4. The process according to any one ofclaims 1 to 3 wherein the monomer (M) is selected from the groupcomprising caprolactam, piperidone, pyrrolidone, laurolactam andmixtures thereof.
 5. The process according to any one of claims 1 to 4wherein the catalyst is selected from the group comprising sodiumcaprolactamate, potassium caprolactamate, bromide magnesiumcaprolactamate, chloride magnesium caprolactamate, magnesiumbiscaprolactamate, sodium hydrides, sodium metal, sodium hydroxide,sodium methoxide, sodium ethoxide, sodium propoxide, sodium butoxide,potassium hydride, potassium metal, potassium hydroxide, potassiummethoxide, potassium ethoxide, potassium propoxide and potassiumbutoxide.
 6. The process according to any one of claims 1 to 5 whereinthe anionic polymerization utilizes an activator.
 7. The processaccording to any one of claims 1 to 6 wherein the foam has a honeycombstructure.
 8. A composite material obtainable by the process of any oneof claims 1 to
 7. 9. The use of a composite material obtainable by theprocess of any one of claims 1 to 7 in sports equipment, as aflameproofing element or as a reinforcing element.